Redirect old readthedocs to new documentation page

[sebix]

migrated from #2517:

People still end up at the wrong documentation site (readthedocs!) Can we automatically redirect them to docs.intelmq.org ?

[aaronkaplan]

how would we do that?
make a job for readthedocs which only contains an explanation that folks should go to docs.intelmq.org?

[sebix]

The first question is, how can we upload data to readthedocs without changing the current and actual documentation here in this repo?
One possibility is to create a second docs-folder here in that repo, or
we could create a separate repository and set that one as the source for intelmq.readthedocs.io.
As the first option could be a source of even more confusion, I'm in favor of the second one.

The new docs in that separate repo then need to contain all the previously existing pages (to not throw 404s) and redirect them all to docs.intelmq.org.